1. Field of the Invention
This invention relates to a rotor with permanent magnets of a rotating machine, or more in particular to a rotor in which a rotor core is integrally formed with permanent magnets arranged on the outer periphery thereof by means of molten metal.
2. Description of the Prior Art
Generally, a ferrite magnet which is superior in magnetic characteristics and low in cost is widely used as a permanent magnet in a rotor. This ferrite magnet, however, is hard and fragile, low in dimensional accuracy, and difficult to process.
In an assembly comprising such a permanent magnet as this arranged around the periphery of a rotor core and bonded thereto by a bonding agent, the permanent magnet is liable to be separated or even flown away from the rotor core, especially when the rotor is driven at high speed. In order to obviate this disadvantage, a rotor in which the surface of the permanent magnets is covered with a protective cover is disclosed in Japanese Patent Laid-Open No. 166755/81 by Takashi Seshita and Hideo Uzuhashi.
Such a proposed rotor is used on an enclosed-type power compressor by being fixed at an end of the rotary shaft coupled to a compression mechanism. This rotor comprises plural permanent magnets arranged along the outer periphery of the rotor core, and the outer peripheries of the permanent magnets are covered with a protective cover, with side covers applied to the upper and lower sides thereof.
A balance weight for correcting the unbalance weight of the compression mechanism is fixed on the outer surface of the side cover. This balance weight is usually fixed on the side cover by welding, screwing or caulking.
When a synchronous motor with such a rotor built therein is driven at high speed, the balance weight develops a great centrifugal force. When this centrifugal force exceeds the fastening force between the balance weight and the side cover, the balance weight is separated from the side cover and flies away to damage the stator coil, causing a fault of the synchronous motor.
The fastening of the balance weight to the protective cover by welding, screwing or caulking depends on working conditions and is not very reliable. In addition, the fastening work takes a long time.